The present invention relates to a hydraulic rack and pinion power steering system including a control valve having an inner valve member (valve core) which is coaxial with and rotatable relative to an outer valve member (valve sleeve).
In this type of steering system, the inner valve member is formed on a part of a cylindrical input shaft which is connected for rotation with the vehicle steering wheel. The outer valve member is connected for rotation with a follow-up member in the form of a pinion. The pinion is in meshing engagement with the toothed portion of a rack. The rack is drivingly connected with a piston-cylinder type power steering motor and steerable vehicle wheels.
To effect actuation of the power steering motor to turn the steerable vehicle wheels, the inner valve member is rotated relative to the outer valve member, from a neutral condition. Relative rotation between the inner and outer valve members ports fluid under pressure to one side or the other of the steering motor to effect steering movement of the steerable vehicle wheels. It is desirable to provide laminar fluid flow and to minimize turbulent fluid flow in the control valve, because turbulence can cause undesirable noise in the steering system.